Polyamide resin composition and method of preparing same



United States Patent POLYAMIDE RESIN COMPOSITION AND METHOD OF PREPARING SANIE N Drawing. Application October 8, 1957 Serial No. 688,843

8 Claims. (Cl. 220-81) The present invention relates to a novel synthetic resin composition and the method of its preparation. More specifically, this invention relates to an adhesive composition derived from two linear polyamide resins and the method of preparing the same.

The instant application is a continuation-in-part of my co-pending application, S. N. 385,887, filed October 13, 1953, now abandoned.

I have discovered that when a hard, tough and brittle polyamide resin made from the copolymerization of an alkylene diamine with certain saturated and unsaturated organic acids is combined in specific proportions with a soft, tacky polyamide resin made from the copolymerization of a polyalkylene polyamine with certain saturated and unsaturated organic acids and this combination of polyamide resins is subjected to heat treatment under controlled conditions, a homogeneous resin composition is produced which at room temperature is very tough, flexible, resistant to solvents and hasexcellent cohesive and adhesive properties.

An object of the present invention is the preparation of a novel polyamide resin composition. I

Another object is the provision of a heat stable, homogeneous composition derived from two different polyamide resins combined in specific proportions.

Yet another object of the invention is the provisio of a tough, rubbery composition having excellent properties of solvent resistance and adhesion for bonding wood, metal, fibre and other materials. s 1

A further object is the provision of a method ofpreparing a heat stable,'homogeneous polyamide resin com position having superior properties as an adhesive.

,Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description which is of a preferred embodiment thereof. 1

Combinations of the soft, flexible, tacky polyamide resin and the tough chemically resistant though brittle polyamide resin are particularly well suited for use as hot melt cements or adhesives. The two resins are compatibleand each confers some desirable properties to the resulting blend. However, such blends change in meltingpoint when held molten for appreciable periods of time. In many industrial applications a change in the melting point of such a hot melt cement or adhesive causes considerable trouble because the set time therefore varies considerably. If the material is applied at 370 F. and the melting point of the blend is 350 F., a relatively small loss of heat will cause the hot melt adhesive to set and to be an effective bonding agent. If, however, the melting point is 330 F. a greater heat loss must occur and, therefore, a longer time must elapse, before the cement sets and can bond the surfaces to be joined. A drift in the melting point is particularly troublesome when the cement is appliedbyvautomatic devices and the parts to bejoined are brought into junction by mechanicallytimed devices at'high'rates of speed and when the -successive partsto be joined follow one. another at very useful in the present invention will be designated short intervals. Any change in melting point results in reduced efficiency of the operation because of premature or late setting or solidification with consequent failures to bond properly. s 4

After extensive experimentation and testing, I discovered that holding a composition containinga major portion of one of the polyamide resinsnand a minor portion of the other at a critical temperature above the melting point of the original composition for a critical periodof time, yielded a product thathas a substantially stable melting point even when in a molten state for extended periods of time. A completely surprising and unexpected result, in addition to thestabilization of the melting point, is'that the heat treated product of the present invention when solidified is considerably more resilient and tougher and becomesasubstantially better adhesive then the comparable l'non-heat treated resin composition. 1 v I I 4 My compositions are well suited as bonding materials for interfolded side seams of sheet metal containers including uncoated steel, i. e. black. plate, and steel having an organic or metal, e. g. tin, coating thereover. Excellent bonds are also produced between aluminum, copper and bronze surfaces. The cohesive strength of my resin compositions and their adhesive strength to metalsrare sufliciently great to enable these compositions to be a satisfactory substitute for metallic solderras' the bonding agent in the side seam of a metal can. Each of the polyamide resins useful in the present invention are prepared, at least in part,,from polymeric fat acids. These polymeric fat acids 'may be either saturated or unsaturated and'may be derived by the thermal polymerization or catalytic polymerization of. higher fatty acids such'as those having 12 to 22 carbon atoms Acids polymeric fat acids and some residual monomer. Some monomer is desirable in the mixed acids for the purpose of controlling'polymer size in the polyamide reaction. Monomer may be either removed from'the polymeric fat acids or added thereto until a desired'quantity. is

present. I

For the purpose of simplicity, the polyamide resins and referred. to hereinafter as resinA and resin B.

-RESINA Resin A is a condensation product of polymericfat acids and a polyalkylene polyamine; Suitable polyalkylene polyamines include diethylene triamine, triethylene tetramine, tetraethylene pentarnine, 3,3'-imino-bispropylamine, and the like. Thus these polyalkylene polyamines contain two primary'amine groups and from I to 3 secondary amine groups, all separated by shortchain alkylene groups having 2 to 4 carbon atoms. The ratio 'of equivalents of polyamine to equivalents of carboxyl should be such that cross linking and hence'gelation are avoided. For example in the case of diethylene triamine a ratio'of 1.5 equivalents of amine to 1 equivalent of carboxyl ispreferred, taking into :account thektotal carboxyl in the'polymeric. fat acid mixture including the monomer as well as the higher polymers present. In the caseof triethylene ,tetrami'ne a higher, amine :ratio such as 2.5

h is about from 4m 11. a

I- and from terephthalic acid at329 -338 F. eral these copolymer polyamide'resins B' are prepared from a mixture of polycarboxylie acids'containing from equivalents of amine per equivalent of carboxyl is preferred. In general, the higher the amine functionality of the polyamine the higher the ratio of amine equivalents per earboxylequivalent that is required to produce .a non-gelling-polyamide. Accordingly, r the particular excess of amine tofb employed in each instance can readily be determined. Usually it is not necessary to go outside the rangeof 1.3 to 3.0 equivalents of amine per 'equivalent of carboxyLjfl/ v Atfroomgtemperature these resins are soft, tacky. and resistant to, greases, oi1s,,water, water vapor, alkali, canpacking brinesand syrups, and a number of organic solvents. The resins have an averagemolecular weight withintherang'e of.2,50.0 to 6,500 and an acid number usually below.10..,. I f

.-The .followingis. example -of thepreparation of a specific .re'sin However, this'example is not to be consideredas aIlimitation ofthe invention merely an explanatiomfor the, better, understanding thereof.

t "Exar'nple; =1 g ,1305 parts of dimerized linoleic acid and 130.5 parts of monomeric cottonseed fatty acids are. uniformly blended in asuitable reaction vessel. The temperature of the mixed acids are then raised about 266F. and .277 parts of'92.6% diethylene triamine is added. At atmospheric pressure and with constant, agitation the temperature of the reaction mass is againelevated to about 392 F. and maintained at this temperature for two hours. A vacuum is then drawn on the vessel and the reaction iscontinued at 392? F. for an additional hour at the reduced pressure. Thereafter the heating is discontinued and the vacuum is brokedwith an inert gas. The finished product may be, maintained in .theteaction-yessel for subsequent use or can be pouredrinto suitable containers to cool and solidify.-- I

This resin has a maximum acid number of 12. The specific gravity. isabout 0.987. and the average molecular weight is betwee'n 3,000 to 6,500. ,Its minimum softening .or meltingpoint as measured by the, ball and ring as a% solution in a 1 .to .1 mixture of butanol and toluene .it has a maximum Gardner-Holdt viscosity of C.

I The typicalcondensation reaction by which' resin A is 'made maybe generally expressed as:

0 'Ho -Bii-NH-+R'NHR'-NH ].H 1.1120 where R is the. hydrocarbon portion of dimerized fat acid,

R .is an alkylene group .having 2 to carbon atoms; and

t u RESIN-1B:

* Resin B is high-meltingQbrittlelpolyamide resin .1...

' rived from a mixture of polymeric fat acids similar to those used in preparingresin-A and an additional polycarboxylie' 'acid, the' latter having at least 2 carboxyl Typicalof such polybasic acids azelaic, and sebacic, and the aromatic acids, terephthalic and isophthalic acids. Instead' of the free acids, the lower aliphatic ester s'or the anhydrides of the polycarboxylic'acid having. a'3'to 8 carbon atom alkylene group may be used. The melting point of the copolymer resin may vary withinthe range of 265-410-F. :depending upon the particular relative reactant ratios 'as well as reaction conditions. Desirable copolymerslfrom adipic acid melt at 392-401 F.; from sebacic acid at 338-374 Ingen- 85-98% by weight of fatty polymeric acids and from 2-15% by weight of the additional polycarboxylic acids. In the preparation of resin B the mixture of polybasic acids is reacted with an alkylene diamine in which the alkylene radical has from 2 to 4 carbon atoms such as ethylene diamine; l, 2- and 1,3-diamino-propane; l,2-, l,3, and 1,4-diamino-butane, and the like. The reactant's are mixed in approximately equivalent quantities and heated under essentially the same conditions as have beeen described'for resin A; Resin B at room temperature is a very hard copolymer which has good resistance togreases, oils, water and water vapor, alkalies, mild acids, can-packing brines and syrups, alcohols, and most organic solvents. The average molecular weight of resin B is from 7,000 to 10,000.

The following is an example of the preparation of a specific resin B. As with the specific example of resin A, the following example should not be interpreted as a limitation of the present invention, merely as an explanation thereof.

Example 2 V In a suitable reaction vessel a uniform blend of acids containing 288.2 parts of dimerized linoleic acid, 31.7 parts of monomeric cottonseed fatty acids and 31.7 parts of sebacic acid is raised to a temperature of about 266 F. To this'heated blend of acids is added 57 parts of 74.5% ethylene diamine and the whole mixture is elevated to a temperature of about 392 F. The reaction mass is preferably agitated to insure intimate contact of the several ingredients. This intimate mixture is maintained at the elevated temperature at atmospheric pressure for about two hours. Thereafter a vacuum is drawn on the vessel and the mass is held at the same elevated temperature for an additional hour under the reduced pressure. The vacuum is then broken with an inert gas and the application of heat discontinued. The finished resin product may be then filled into suitable containers and allowed to cool.

This resin has a'maximum acid number of'15 and a specific gravity of about 0.966. Its minimum softening or melting temperature as measured by the ball and ring test (A. S. T. M.) isabout 343 F. A 25% solution of resin B in a 1 ml mixture of butanol and phenol has 'a viscosity of A to C on the Gardner-Holdt scale.

The general reaction shown for resin A may also be applied to resin B except an alkylene diamine is substituted for the dialkylene triamine used for resin Aand n is about from 12 to .17.

Although the reaction causing the melting point drop of the polyamide resin blends is not completely understood, it-is known to be an amide interchange reaction between the, different, nitrogen-containing portions of the resin and resin B, molecules. By this reaction the original components of the composition react with one another forming new compounds which produce a composition having different properties from the original combination. i

In this reaction it is believed thatsome of the alkylene diamine groups of resinBinterexchange with some of the polyalkylene polyamine groups of resin A. This exchange of amines between resin A and resin B takes place in two stages Stage one is believed to be the exchange of'the end groupamines andtakes place rapidly at temperatures above about'392" F. The reaction occurring during stage. one continues until the exchange of available end groupamines reaches an equilibrium which can be 'called exchange equilibrium. During the stage one reaction the melting point of a blend ofresin A and resin B drops rapidly. The end point of this reaction is evidenced by a sharp decline inthe rate ofreaction or, as a more-commonly used reference, by a sharp break or leveling off in a curve obtained by plotting, on rectangular coordinates, Ball and ring melting points against time. As indicated by thislast mentioned curve,

at the end .ofthestage one reaction .the melting ;.point decline of the compositionhas substantially ceased, and a composition having a relatively stable melting point is obtained.

Stage two of the reaction is believed to be an exchange of the internal amine groups in the resin A and resin B molecules. This exchange of internal amines does not take place as readily as the exchange of terminal amine groups. Thus after the completion of the stage one reaction, the melting point of the blend held in a molten state drops very slightly over a period of time.

In carrying out the process of the present invention resin A and resin B are combined in the appropriate ratio and intimately mixed to insure a uniform, homogeneous blend when molten. Thereafter the homogeneous blend of the two resins'is maintained at a temperature above the melting point of the original composition for a time sufiicient to effect stage one of the amide interchange reaction whereby the melting point of the composition is stabilized.

For the adhesive composition of the present inven-.

tion having the desirable properties and utility disclosed herein, the operable weight ratios of the two polyamide resins were found to be in the range of from 50/50 to 75/25 resin A to resin B respectively and preferably a ratio of 65/35 resin A to resin B. After extensive experimentation, it was found that if the amount of resin A is greater than 75% of the composition, the resulting adhesive is too soft and lacks sufiicient cohesive strength; and if the amount of resin A is less than50% of the composition, the resulting adhesive is brittle and frac tures easily.

The blending operation may be carried out in many ways, it being necessary only that an intimate, homogeneous blend of the two resins may be obtained. For example, a satisfactory blend can be made by adding resin A to molten resin B. I have found it more practical however to add resin B to molten resin A since it is difiicult and time consuming to melt the solid resin B separately without the accompanying danger of localized overheating.

The preferred method of blending the two resins is by adding pieces, egg size or smaller, of resin B to molten resin A held at a temperature at or above 400 F. Agitation of the mixture is required to insure that a homogeneous blend is obtained. In order to prevent oxidative deterioration of the resins they are blanketed by an inert atmosphere such as nitrogen or carbon dioxide while they are maintained at these elevated temperatures.

Satisfactory blending can be accomplished at temperatures from 400 F. to 550 F. and preferably from 400 F. to 420 F. If blending is done below 400 'F. the components lack sufiicient fluidity for intimate mixing whereby a non-homogeneous composition results. When such non-homogeneous blends are then held molten at temperatures close to the melting point of the composition, the higher melting aggregates of resin B have a tendency to separate and form gel particles in the mass. If too high a temperature is maintained during blending, the first portions of resin B to melt take part in the amide interchangereaction to an excessive degree before the entire amount of resin B added becomes molten.

' During the blending operation, it is necessary only to allow suflicient time to insure a homogeneous blend. Under this condition, the time. interval is dependent upon the temperature of blending, thesize of the resin B pieces added and the efficiency of agitation. I have found that by adding egg size or smaller pieces of resin B to molten resin A at about 400 F. using a mechanical- 'ly operated agitator, a time interval of about 30 to 60 minutes is suflicient.

In the heat treating operation, both the temperature too rapidly to be followed or controlled at temperatures above 450 F. About 16 .hours is needed to complete the reaction at 392 F. while 'at 450 F. a time of about one hour is sutficient. Therefore, a range of from 392 F. to 450 F. and preferably about 425 F. is required for the heat treatment of the resin blend.

The original melting point of blends of resin A and resin B within the scope of my invention varies over a range of about 340 F. to about 360 F. In carrying out the heat treatment, the blend is held with agitation between 392 F. and 430 F. to effect the amide inter.- change reaction with its resulting melting point drop of the blend. A sample is withdrawn from the. reaction vessel about every fifteen minutes during the process and a ball and ring melting point determination taken thereof to follow the course of the reaction as indicated by the melting point drop. This procedure is continued until it is found that the rate of drop of the melting point has decreased sharply. This usually occurs when the melting point of the composition has reached about325 F. Heating is then discontinued and the resin composition is removed from the reaction vessel and packaged for subsequent use.

The following example is for the purpose of specifically showing my invention and is not intended as a limitation thereon. The resin A and resin B disclosed in this example are the specific resin and resin Bset forth in Examples l and 2 respectively.

Example 3 Into a suitable reaction kettle equipped with a mechanical agitator and means for excluding atmospheric air 39 pounds of resin A were charged. The charge was then blanketed with an atmosphere of nitrogen and heat applied to the kettle to raise the temperature-of the charge to 420 F. When the resin A became sufliciently fluid,

at approximately 200 F., the agitator was, started. Upon reaching the 420 F. temperature, 21 pounds of resin B reduced to egg size or smaller pieces were charged into the kettle while maintaining the inert atmosphere and agitation. Elapsed reaction time is measured from this point.

This blend of resin A and resin B was found to have an original ball and ring melting point of 353 F. After about 30 minutes the blend appeared to be homogeneous and a sample ofthis blend was found to havea ball and ring melting point of 350 F. The temperature of the mass was maintained at about 424 F. with constant agitation and samples were taken every fifteen minutes vto determine the ball and ring melting point thereof.

The results are tabulated as follows:

45 minuteq 347 60 minutes 345 75 minutes 340 minutes 335 minutes 330 At this point the reaction had nearly reached exchange equilibrium as indicated by previously established ball and ring melting point vs. time curves referred to hereinbefore and heating was discontinued and drumming off of the composition begun. The drumming off consumed an additional thirty-five minutes during which time the temperature of the blend dropped to about 400 F. A ball parts of the resin A of Example 1 and 35 parts of the resin B of Example 2. The melting point change data given below was determined at 370 F. since this is the e temPQIQ IQLQt wh t h the composition of; the present in- .Property Heat Non-Heat Treated Treated Ball audfR-ing MeltinlgPoint in F 310325 340 360 Rex Hardness at70 85 90 Poll Bt'rmgth .at 180 angle of bonded sheet metal stripspulled over rollers in pounds per "%lineal inch... 38.5 33.8 Mooney Viscosity at 190 F 36 28 Mooney Elastic Recovery at 190 FA 38 15 Impact Resistance of Free Film at room temperature inlt. pounds- 1. 8 '1. 3 Rate of melting oint decline in degrees per 7 hour when he] at 370 F a 1 From the above it can be seen that: the peel strength is increased approximately resistance to fracture under impact is improvedapproximately 40%; elasticity and toughness as shown by Mooney elastic recovery and Mooney viscosity are, improved approximately 150% and 29% respectively; flexibility is improved as shown by a decrease of 5 of the Rex Hardness; and the stability of the melting point is greatly improved.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and that various changes and modifications may be apparent to one skilled in the art without depart- 'ing from the spiritand scope of the invention or sacrificirig its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

sisting essentially ofthe polyacyl groups of a polymeric fatjjacid and the polyamino groupsof a polyalkylene polyamine having terminaltprimary amino groups, and

;about to 50% by weight of a polyamide resin B consisting essentially'of the mixed polyacyl groups of a polymeric fat acid and a 3 to 8 carbon atom dicarboxylic acid free from ethylenic unsaturation. and the diarnino groups of an" alkylene diprimary diamine, said mixed polyacyl groups resulting from a ratio of 85% to 98% :by weight of said polymeric fat acid to 2% to 15% by weight of'said dicarboxylic acid, said reaction product jbeing'for'med by mixing and maintaining said polyamide resins A and B at a temperatureof about 392 F. to

450F. for a time of about 71 to 16 hours, the longer time being used with the lpwer temperature.

.' 72, A resin composition comprising the reaction product .of about 50% to 75%fby weight of a polyamidc resin A consisting essentially. of the polyacyl groups of a polyacid free from ethylenic unsaturation and the diamino groups of alkylene diprimary diamine, said mixed polyacyl groups resulting from. a ratio of 85% to- 98% by weight of said polymeric fat acid to 2% to 15% by weight of said dicarboxylic acid, said reaction product being formed by mixing andinaintaining said polyamide *resins ,A and B at, a temperature of about 392 F. to 450 F. fora time of about 1 to '16 hours, the longer time being usfed with the lower temperature.

. 3. Ares'incomposition comprising the reaction product of about 50 -to 75% by weight of a polyamide resin' .35 l. A resincomposition comprising the reaction 'product of ab0ut"50% to 75% of a,polyamide resin A com- A consistingessentially .of the polyacyl groups of a polymeric fat acid .and the triamino groups of diethylenetriamine, and about 25% to 50% by weight of a polyamide resin :B;consistingcsseutially of the mixed polyacyl groups of a polymeric fat-acid and sebacic acid and thediamino groups of ethylene diamine, said mixed-polyacyl groups resulting from a ratio of 85% to 98% by weight of said polymeric fat acid to 2% to 15% by weight of said sebacic acid, said reaction product being formed by mixing and maintaining said polyamide resins A and B at a temperature of about 392 F. to 450 F. for a time of about 1 to 16 hours, the longer time being used with the lower temperature.

4. A resin composition comprising the reaction'product of about 50% "to by weight of a polyamide resinA consisting essentially of the polyacyl groups of dilinoleic acid and the triamino groups ofdiethylene tr'iamine, and about 25% to 50% by weight of a polyamide resin B consisting essentially of the mixed polyacyl groups of dilinoleic acid and sebacic acid and the diamiuo groups of ethylene diamine, said mixed polyacyl groups resulting from a .ratio of about90% by weight of said dilinoleic acid to about 10% by Weight of said sebacic acid, said reaction product being formed by mixing and maintaining said polyamide resins A and B at a temperature of about 424 F. for a time of about 1 hour, 45 minutes and for an additional 35 minutes while said temperature decreases to about 400 F. I

I 5. A process comprising intimately blending about 50% to 75 of a polyamide resin consisting essentially of the polyacyl groups of a polymeric fat acid and the polyamino groups of a polya'lkylene polyamine having terminal primary amino groups, and about 25% to 50% by weight of a polyamide resin consisting essentially of the mixed polyacyl groups of a polymeric fat acid and a 3 to 8 carbon atom dicarboxylic acid free from ethylcnic unsaturation andthe diamino groups of an alkylene diprimary diamine,said mixed polyacyl groups resulting from aratio of to 98% by. weight of said polymeric fat acid to 2% to 15 by weight of said dicarboxylic acid, and subjecting said blendto a temperature of 392 F. to 450 F.,-for-a time of about 1 hour to 16 hours, the longer time being used with the lower temperature.

6. A process comprising heating to a temperature of from 400 F. to 420 F. in an inert atmosphere and thereby melting a polyarnide resin A consisting essentially of the polyacyl group of dilinoleic acid and the triamino groups of dicthylene triamine, adding to said molten resin with constant agitation a polyamide resin B consisting essentially of the mixed polyacyl groups of dilinoleic acid and sebacic acid and the diamino groups of ethylene diamine to form a blend, said mixed polyacyl groups resulting from aratio of %of said dilinoleic acid to 10% of said sebacic acid, said blend containing 50% to 75 of said polyamideresin A and 25% to 50% of said polyamide resin B, and subjecting theblend to a temperature of about 424 F. for a time of about 1 hour, 45 minutes and thereafter for an additional 35 minutes while said temperature decreases to about 400 F.

7. A plurality of metal layers having the composition of claim 1 between adjacent surfaces thereof as a bonding material therefor.

8. A metal container having the composition of claim 1 enclosed within the side seam thereof as the bonding material therefor.

References Cited in the file of this patent .UNITED STATES PATENTS 

1. A RESIN COMPOSITION COMPRISING THE REACTION PRODUCT OF ABOUT 50% TO 75% OF A POLYAMIDE RESIN A CONSISTING ESSENTIALLY OF THE POLYACYL GROUPS OF A POLYMERIC FAT ACID AND THE POLYAMINO GROUPS OF A POLYALKYLENE POLYAMINE HAVING TERMINAL PRIMARY AMINO GROUPS, AND ABOUT 25% TO 50% BY WEIGHT OF A POLYAMIDE RESIN B CONSISTING ESSENTIALLY OF THE MIXED POLYACYL GROUPS OF A POLYMERIC FAT ACID AND A 3 TO 8 CARBON ATOM DICARBOXYLIC ACID FREE FROM ETHYLENIC UNSATURATION AND THE DIAMINO GROUPS OF AN ALKYLENE DIPRIMARY DIAMINE, SAID MIXED POLYACYL GROUPS RESULTING FROM A RATIO OF 85% TO 98% BY WEIGHT OF SAID POLYMERIC FAT ACID TO 2% TO 15% BY WEIGHT OF SAID DICARBOXYLIC ACID, SAID REACTION PRODUCT BEING FORMED BY MIXING AND MAINTAINING SAID POLYAMIDE RESINS A AND B AT A TEMPERATURE OF ABOUT 392*F. TO 450*F. FOR A TIME OF ABOUT 1 TO 16 HOURS, THE LONGER TIME BEING USED WITH THE LOWER TEMPERATURE. 